Show files opened by pytest tests

My test suite for Datasette has grown so large that running the whole thing sometimes causes me to run out of file handles.

I've not solved this yet, but I did figure out a pattern to get pytest to show me which new files were opened by which tests.

Add the following to conftest.py:

import psutil


@pytest.fixture(autouse=True)
def check_for_new_file_handles(request):
    proc = psutil.Process()
    before_files = set(proc.open_files())
    yield
    after_files = proc.open_files()
    new_files = [f for f in after_files if f not in before_files]
    if new_files:
        print("{} opened by {}".format(new_files, request.node))

This uses psutil (pip install psutil) to build a set of the open files before and after the test runs. It then uses a list comprehension to figure out which file handles are new.

Using @pytest.fixture(autouse=True) means it will automatically be used for every test.

It's a yield fixture, which means the part of the code before the yield statement runs before the test, then the part afterwards runs after the test function has finished.

Accepting the request argument means it gets access to a pytest request object, which includes request.node which is an object representing the test that is being executed.

You need to run pytest -s to see the output (without the -s the output is hidden).

Example output:

tests/test_permissions.py .[popenfile(path='/private/var/folders/wr/hn3206rs1yzgq3r49bz8nvnh0000gn/T/tmp76w2ukin/fixtures.db', fd=8)] opened by <Function test_view_padlock[/-None-200-200]>..

Created 2022-12-11T16:08:45-08:00 · Edit

Show files opened by pytest tests

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